Some more feedback after some more testing.
Make presets remember/store all the settings 1 until 6 including the additional command line parameters and launch options. At the moment a preset only remembers 1, 2, 3, 6 from what I can see. For example my use case would be setup a new preset with mappack Eviternity launching under PrBoom-plus with command line -complevel 11. And another preset for mappack Scythe, -complevel 2. This is not possible at the moment since it doesn't store the mappacks and command line in presets.
Same goes for launch options, for example WAD Eternal Doom IV starts only on map 8. But launch options gets stored globally instead of per preset which means I'll have to remember which WADs contain which levels and manually change every time I want to play that WAD.
Another suggestion would be to be able to select multiple WADs in the map selection, for example Back to Saturn Episodes uses multiple WADs. Epic use multiple WADs (one for GL Skies). The Darkening, Alien Vendetta, Memento Mori, Valiant, etc all use multiple WAD files, wether it be for music or GL skies or something else.
Unless I misunderstand the functionality and function of mappacks section. Maybe if it's only supposed to be for official expansions? And the MOD section for the rest? I'd suggest a renaming them then, because it is confusing.
Hopefully you can get some ideas and inspiration from https://gitlab.com/sdcofer70/enyo-doom
Since it also uses C++ and Qt and it has functioning presets and profiles which stores all relevant options.
Other than that it's very lightweight, fast, and has a lot of functionality. Great work.